Hypophosphatemia in Critically Ill Children: Risk Factors, Outcome and Mechanism

Abstract

Objectives: To determine the prevalence of hypophosphatemia in critically ill children and its association with clinical outcomes; to determine risk factors and mechanism of hypophosphatemia.

Methods: Levels of serum phosphate, phosphate intake, renal phosphate handling indices and blood gases were measured on days 1, 3, 7 and 10 of pediatric intensive care unit (PICU) stay. Hypophosphatemia was defined as any serum phosphorus <3.8 mg/dl for children younger than 2 y and <3.5 mg/dl for children 2 y or older. Renal phosphate loss was assessed using the ratio of tubular maximum reabsorption of phosphate (TmP) to glomerular filtration rate (GFR) [TmP/GFR].

Results: Prevalence of hypophosphatemia was 71.6 % (95 % CI: 64.6-78.6). On adjusted analysis, hypophosphatemia was associated with prolonged PICU length of stay (PICU LOS > 6 d) (adjusted OR: 3.0 [95 % CI: 1.4-6.7; p = 0.005]) but not associated with increased mortality. Renal phosphate threshold was significantly lower on all the days in hypophosphatemic group compared to that of non-hypophosphatemic group. No statistically significant difference in the amount of phosphate intake was seen in both the groups.

Conclusions: Hypophosphatemia is highly prevalent in critically ill children and is associated with prolonged PICU LOS. Increased phosphate loss in urine is one of the mechanism responsible for hypophosphatemia in critically ill children.

Keywords: Children; Critical illness; Hypophosphatemia; Length of stay; Outcomes; Phosphaturia.